The present invention relates to disk drives. More particularly, it relates to a method and apparatus for an in-situ head-disk interface evaluation based upon transient MR head heat flux detection.
A magnetic disk drive apparatus is an apparatus for recording and reading data on the surfaces of spinning disks through the use of a changing magnetic field. One or more data storage disks are coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand to tens of thousands of revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator assembly and hover above the surface of the rapidly rotating disks.
The transducer head is typically in the form of a magnetoresistive (MR) read element and/or an inductive write element carried on a slider body. Oftentimes, the slider and transducer are referred to in combination as a xe2x80x9cheadxe2x80x9d. Regardless, writing data to a disk generally involves passing a current through the write element of the transducer to produce magnetic lines of flux that magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by the read element sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals, commonly referred to as readback signals, in the read element.
The slider is typically mounted to a flexible suspension portion of an arm assembly that is otherwise part of the actuator assembly. Further, the slider normally incorporates a rail or pad design that facilitates formation of an air bearing upon rotation of the disk. More particularly, as the disk rotates, an air bearing develops between the slider and the disk surface, causing the slider, and thus the read/write head, to lift and fly several microinches above the disk surface. The distance between the slider and the disk surface is oftentimes referred to as a xe2x80x9cfly heightxe2x80x9d. In magnetic recording technology, it is desired to xe2x80x9cflyxe2x80x9d the slider as closely as possible to the disk surface (i.e., minimal fly height) so that the read transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk. The combination of the head and the disk surface is commonly referred to as the head-disk interface (HDI).
Disk drive manufacturers are continually searching for improved methods of performing in-situ HDI evaluations (i.e., in an operational disk drive following final assembly). As the HDI deteriorates, the opportunity for unexpected contact between the transducer head and the disk surface (or xe2x80x9chead crashxe2x80x9d) increases significantly. Obviously, a head crash is highly undesirable as it results in loss of data, damage to the disk, damage to the transducer head, etc. To this end, accepted techniques have revolved around attempting to determine the actual operational fly height, and then evaluating whether the fly height is below an acceptable level. Unfortunately, available fly height measuring systems are relatively expensive to implement, time consuming, and imprecise, especially for operational disk drives. With respect to MR-transducer heads, efforts have been made to convert the magnetic signal induced in the MR transducer to a spacing signal that varies as a function of head-to-disk spacing changes. Again, however, these techniques are relatively time consuming, may require a specially formatted track on the disk, etc. These deficiencies are further exacerbated with recently available glass-based disks. With glass disks, the operational fly height is much less than the fly height associated with aluminum-based disks due to the highly planar disk surface afforded by glass. As a result, the uncertainty associated with any one particular fly height measurement technique increases dramatically, necessitating further, and thus costly, measurement technique improvements.
Operational disk drive HDI evaluation continues to be highly important. However, existing techniques based upon monitoring changes in fly height are not cost effective and do not produce consistent results, especially with glass-based disks. Therefore, a need exists for an inexpensive method and apparatus for evaluating, in-situ, operational disk drive HDI based upon available signal information.
One aspect of the present invention relates to a method of evaluating a condition of a head-disk interface (HDI) of an operational disk drive. The disk drive includes at least one disk having a disk surface and at least one MR transducer head for reading data from the disk surface. In this regard, the MR transducer head is sensitive to temperature changes. With this in mind, the method includes rotating the disk at an operational rate. A first thermal signal is received from the MR transducer head that is indicative of temperature at the transducer head. The first thermal signal is analyzed for thermal transients. Based upon this analysis, first thermal variation information indicative of a relationship of thermal transients in the first thermal signal relative to a baseline is generated. Finally, the first thermal variation information is compared to threshold information indicative of an acceptable HDI. In one preferred embodiment, a prediction of an impending head crash is made based upon the comparison. Regardless, the method of the present invention does not attempt to calculate a fly height. Instead, the method essentially monitors thermal activity, and in particular thermal transients, at the transducer head. As described herein, this thermal transient information is directly related to the health of the HDI, and is therefore a better head crash predictor than existing methodologies.
Another aspect of the present invention relates to a disk drive including at least one disk, at least one transducer head, a spindle motor, an actuator assembly, and a programmable controller. The disk has a disk surface. The MR transducer head is provided for reading data from the disk surface. In this regard, the transducer head is temperature sensitive and generates a readback signal, a component of which is indicative of temperature at the transducer head. The spindle motor is coupled to the disk for rotating the disk. The actuator assembly is coupled to the transducer head for positioning the transducer head over the disk surface. Finally, the programmable controller is configured to evaluate an interface between the transducer head and the disk surface (HDI). In this regard, the programmable controller is capable of receiving the readback signal from the transducer head and delineating a thermal component signal therefrom. The programmable controller is further capable of analyzing the thermal component signal for thermal transients and generating thermal variation information indicative of a relationship of the thermal transients relative to a baseline. Finally, the programmable controller is capable of comparing the thermal variation information to threshold information that is otherwise indicative of an acceptable HDI, and then evaluating a current status of the HDI based upon this comparison. In one preferred embodiment, the disk is glass-based, and the programmable controller is capable of evaluating the HDI at any radial position of the transducer head relative to the disk surface.